1. Field of the Invention
The present invention relates to an emission control driver and an organic light emitting display using the same, and more particularly, to an emission control driver including emission control signal generating circuits that generate emission control signals using scan signals and an organic light emitting display using the same.
2. Discussion of the Background
An organic light emitting diode (OLED) may include a light emitting thin film emission layer arranged between a cathode electrode and an anode electrode. Electrons and holes are injected into the emission layer where they are recombined to emit light.
The emission layer of an OLED or IOLED may be formed of organic or inorganic material. OLEDs may be classified as either inorganic or organic according to the type of emission layer used.
FIG. 1 illustrates part of a conventional organic light emitting display. Referring to FIG. 1, a pixel includes an OLED and a pixel circuit. The pixel circuit includes a first transistor M1, a second transistor M2, and a capacitor Cst. Each of the first M1 and second M2 transistors includes a gate, a source, and a drain. The capacitor Cst includes a first electrode and a second electrode.
The source of the first transistor M1 is coupled with a power source supply line Vdd to receive a pixel power source, the drain of the first transistor M1 is coupled with the anode of the OLED, and the gate of the first transistor M1 is coupled with a first node A. The first node A is coupled with the drain of the second transistor M2. The first transistor M1 supplies current corresponding to a data signal to the OLED.
The source of the second transistor M2 is coupled with a data line Dm, the drain of the second transistor M2 is coupled with the first node A, and the gate of the second transistor M2 is coupled with a first scan line Sn. The second transistor M2 transmits the data signal to the first node A in accordance with the scan signal applied to the gate of the second transistor M2.
The first electrode of the capacitor Cst is coupled with the power source supply line Vdd and the second electrode of the capacitor Cst is coupled with the first node A. The capacitor Cst stores a predetermined voltage in response to the data signal and applies the stored voltage between the gate and source of the first transistor M1 for one frame so that the operation of the first transistor M1 is maintained for one frame.
In a pixel having the above structure, the voltage stored in the capacitor Cst is transmitted to the gate of the first transistor M1 so that current flows to the OLED through the first transistor M1. The voltage between the gate and source of the first transistor M1 and the current that flows to the OLED by the capacitor Cst correspond to EQUATION 1.
                              Vgs          =                      Vdd            -            Vdata                          ⁢                                  ⁢                                                                              I                  OLED                                =                                                      β                    2                                    ⁢                                                            (                                              Vgs                        -                        Vth                                            )                                        2                                                                                                                          =                                                      β                    2                                    ⁢                                                            (                                              Vdd                        -                        Vdata                        -                        Vth                                            )                                        2                                                                                                          [                  EQUATION          ⁢                                          ⁢          1                ]            
where Vgs represents the voltage between the gate and source of the first transistor M1, Vdd represents the voltage of the pixel power source, Vdata represents the voltage of the data signal, Vth represents the threshold voltage of the first transistor M1, and β represents the gain factor of the first transistor M1.
However, as represented in the EQUATION 1, the current that flows to the OLED corresponds to the threshold voltage of the first transistor M1. Therefore, non-uniformity in brightness may be due to non-uniformity in the threshold voltage of the first transistor M1 generated during the processes of fabricating the light emitting display. This may cause the picture quality of the display to deteriorate.